The existing transmission systems for converting torque from an input shaft to a load-varying output shaft operate on the step-by-step principle which consists of achieving a predetermined output speed by passing through a series of fixed speed levels. The number of steps required depends on the rotational speed of the drive shaft and the load actually applied to the output shaft.
In these presently existing transmission mechanisms, the power flow, when the transmission is "in gear", is a single stream either through different meshing gears and shafts (when in low gear) or, generally, through a direct drive connection (when in high gear). The transmission gear ratio is a constant, the ratio being the speed of the input shaft to the speed of the output shaft for that particular gear. Therefore, the value of each gear shift ratio in a standard transmission is a constant which is a function of all the individual gear pair ratios engaged at that moment. In other words, the connection between the engine and the driven wheels is fixed, since any change in the engine rotational speed entails a proportional change in the rotational speed of the wheels.